Re: SRV Request to DNS

[Anders Löwinger]

Den 2015-10-14 kl. 17:29, skrev Barry Margolin:

Are there*any*  current, well-known protocols that make use of SRV
records to find the port? The examples I've seen just use it to find a
server (analogous to the way MX records are used for mail).


Examples:

SIP
http://www.voip-info.org/wiki/view/DNS+SRV

XMPP
http://wiki.xmpp.org/web/SRV_Records


/Anders

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Re: SRV Request to DNS

[Barry Margolin]

In article ,
 Mark Andrews  wrote:

> To answer the question.  What you do when given a name and a port
> is protocol specific.  Read the protocol specification.  Note if
> the port is the well known port for the protocol then it may be
> ignored.
> 
> If the protocol does not specify most developers will just implement
> the protocol over that port to the specified host taking into account
> well known ports if needed.
> 
> To used SRV with a protocol you need a specification that says to
> do so.  Using SRV without such a specification results in undefined
> behaviour.

Are there *any* current, well-known protocols that make use of SRV 
records to find the port? The examples I've seen just use it to find a 
server (analogous to the way MX records are used for mail).

Theoretically, this could be useful for HTTP, so you wouldn't have to 
put :port# in URLs if the domain uses an alternate port. It would make 
things easier when you have servers for multiple domains behind a NAT 
router with a single public address. But AFAIK there's been no movement 
to require browsers to use SRV for this.

-- 
Barry Margolin
Arlington, MA
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Re: SRV Request to DNS

[Alan Clegg]

On 10/14/15 11:29 AM, Barry Margolin wrote:

> Are there *any* current, well-known protocols that make use of SRV 
> records to find the port? The examples I've seen just use it to find a 
> server (analogous to the way MX records are used for mail).

I guess it depends on what you define as a well-known protocol...

Teamspeak 3:
https://support.teamspeakusa.com/index.php?/Knowledgebase/Article/View/293/12/does-teamspeak-3-support-dns-srv-records

AlanC
-- 
When I do still catch the odd glimpse, it's peripheral; mere fragments
of mad-doctor chrome, confining themselves to the corner of the eye.



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Re: SRV Request to DNS

[Bob Harold]

On Wed, Oct 14, 2015 at 11:40 AM, Anders Löwinger  wrote:

> Den 2015-10-14 kl. 17:29, skrev Barry Margolin:
>
> Are there **any** current, well-known protocols that make use of SRV
> records to find the port? The examples I've seen just use it to find a
> server (analogous to the way MX records are used for mail).
>
>
> Examples:
>
> SIP
> http://www.voip-info.org/wiki/view/DNS+SRV
>
> XMPP
> http://wiki.xmpp.org/web/SRV_Records
>
>
> /Anders
>
> Kerberos
http://web.mit.edu/kerberos/krb5-1.6/krb5-1.6.3/doc/krb5-admin.html#Hostnames-for-KDCs
--- But not sure if the 'port' is actually used, since it can also be
defined in the conf file.

-- 
Bob Harold
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Re: SRV Request to DNS

[Mark Andrews]

In message <561e91ed.3060...@clegg.com>, Alan Clegg writes:
>
> > Are there *any* current, well-known protocols that make use of SRV
> > records to find the port? The examples I've seen just use it to find a
> > server (analogous to the way MX records are used for mail).
>
> I guess it depends on what you define as a well-known protocol...
>
> Teamspeak 3:
> https://support.teamspeakusa.com/index.php?/Knowledgebase/Article/View/293
> /12/does-teamspeak-3-support-dns-srv-records
>
> AlanC
> --
> When I do still catch the odd glimpse, it's peripheral; mere fragments
> of mad-doctor chrome, confining themselves to the corner of the eye.

All protocols that use SRV do.  It's the operators that decide the
port to put in the SRV record, not the protocol.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org
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Re: SRV Request to DNS

[Chris Buxton]

On Oct 5, 2015, at 11:51 PM, Harshith Mulky  wrote:
> Let us say we are having a FQDN and we need to Resolve it. It goes through 
> the procedure of determining the IP and Port using NAPTR/SRV/A query 
> mechanisms
> 
> The question I have is if I have a FQDN with a Port Number already 
> determined, will it go through the Procedure of NAPTR/SRV/A query (or) simply 
> do a A query (or) Is this left to the client to apply the Logic?

The client must supply the logic. DNS is conceptually a simple database service 
— ask a question, get an answer. The logic of using NAPTR records, SRV records, 
A records,  records, and CNAME records is mostly handled by the client. 
(CNAME and DNAME records are the primary exception, triggering extra processing 
on the recursive name server.)

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Re: SRV Request to DNS

[Mark Andrews]

To answer the question.  What you do when given a name and a port
is protocol specific.  Read the protocol specification.  Note if
the port is the well known port for the protocol then it may be
ignored.

If the protocol does not specify most developers will just implement
the protocol over that port to the specified host taking into account
well known ports if needed.

To used SRV with a protocol you need a specification that says to
do so.  Using SRV without such a specification results in undefined
behaviour.

This really isn't a DNS question.  The DNS is just the database
that stores the values that are being looked up.

Mark


In message <d5ff3ef51b504cca9d832b056043d...@mxph4chrw.fgremc.it>, "Darcy Kevin
 (FCA)" writes:
> 
> Harshith,
> I think you need to understand the proportionality here: the
> *vast*majority* of the time, the client already knows the port (because
> ports tend to be pre-assigned for specific services), and only needs to
> resolve the FQDN to one or more address records (A and/or  records),
> in order to make a connection. This isn't really a burden, or complicated
> logic in the client software, since it can just call a generic hostname
> lookup function (e.g. the traditional gethostbyname() or the more modern
> getaddrinfo()). It's not like every application programmer needs to deal
> with parsing packet contents, handling retries, dealing with label
> compression, etc. This is all handled in the library routine.
>
> Only in a small minority of cases do clients go through the whole NAPTR
> or SRV process. Some of the main scenarios for that include:
>
> * Microsoft Active Directory. The clients use SRV records as part
> of the so-called "dc locator" process to find a domain controller that
> provides a specific service
>
> * Certain IM clients (like Lync) use SRV records to find SIP
> services
>
> * SIP telephony clients use NAPTR records
>
> Note that SMTP clients use MX records rather than SRV records. MX records
> can be considered the simpler, mail-specific precursor to SRV records.
> Theoretically, SMTP _could_ be switched over to use SRV records, but the
> use of MX is so ingrained that it's probably not worth the (massive)
> effort.
>
> If you look at nameserver query statistics, you'll see that the volume of
> SRV and/or NAPTR queries on a typical nameserver/resolver is a miniscule
> fraction of the A/ traffic. Where MX-record traffic falls between
> those extremes, will depend a lot on whether the nameserver/resolver is
> internal or external, whether the particular domain is heavily used for
> mail, etc.
>
>
>
> - Kevin
>
> From: bind-users-boun...@lists.isc.org
> [mailto:bind-users-boun...@lists.isc.org] On Behalf Of Chris Buxton
> Sent: Tuesday, October 13, 2015 7:58 AM
> To: Harshith Mulky
> Cc: BIND Users
> Subject: Re: SRV Request to DNS
>
> On Oct 5, 2015, at 11:51 PM, Harshith Mulky
> <harshith.mu...@outlook.com<mailto:harshith.mu...@outlook.com>> wrote:
> Let us say we are having a FQDN and we need to Resolve it. It goes
> through the procedure of determining the IP and Port using NAPTR/SRV/A
> query mechanisms
>
> The question I have is if I have a FQDN with a Port Number already
> determined, will it go through the Procedure of NAPTR/SRV/A query (or)
> simply do a A query (or) Is this left to the client to apply the Logic?
>
> The client must supply the logic. DNS is conceptually a simple database
> service - ask a question, get an answer. The logic of using NAPTR
> records, SRV records, A records,  records, and CNAME records is
> mostly handled by the client. (CNAME and DNAME records are the primary
> exception, triggering extra processing on the recursive name server.)
>
> Chris
>

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org
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RE: SRV Request to DNS

[Darcy Kevin (FCA)]

Harshith,
I think you need to understand the proportionality here: the *vast*majority* of 
the time, the client already knows the port (because ports tend to be 
pre-assigned for specific services), and only needs to resolve the FQDN to one 
or more address records (A and/or  records), in order to make a connection. 
This isn't really a burden, or complicated logic in the client software, since 
it can just call a generic hostname lookup function (e.g. the traditional 
gethostbyname() or the more modern getaddrinfo()). It's not like every 
application programmer needs to deal with parsing packet contents, handling 
retries, dealing with label compression, etc. This is all handled in the 
library routine.

Only in a small minority of cases do clients go through the whole NAPTR or SRV 
process. Some of the main scenarios for that include:

* Microsoft Active Directory. The clients use SRV records as part of 
the so-called "dc locator" process to find a domain controller that provides a 
specific service

* Certain IM clients (like Lync) use SRV records to find SIP services

* SIP telephony clients use NAPTR records

Note that SMTP clients use MX records rather than SRV records. MX records can 
be considered the simpler, mail-specific precursor to SRV records. 
Theoretically, SMTP _could_ be switched over to use SRV records, but the use of 
MX is so ingrained that it's probably not worth the (massive) effort.

If you look at nameserver query statistics, you'll see that the volume of SRV 
and/or NAPTR queries on a typical nameserver/resolver is a miniscule fraction 
of the A/ traffic. Where MX-record traffic falls between those extremes, 
will depend a lot on whether the nameserver/resolver is internal or external, 
whether the particular domain is heavily used for mail, etc.



- Kevin

From: bind-users-boun...@lists.isc.org 
[mailto:bind-users-boun...@lists.isc.org] On Behalf Of Chris Buxton
Sent: Tuesday, October 13, 2015 7:58 AM
To: Harshith Mulky
Cc: BIND Users
Subject: Re: SRV Request to DNS

On Oct 5, 2015, at 11:51 PM, Harshith Mulky 
<harshith.mu...@outlook.com<mailto:harshith.mu...@outlook.com>> wrote:
Let us say we are having a FQDN and we need to Resolve it. It goes through the 
procedure of determining the IP and Port using NAPTR/SRV/A query mechanisms

The question I have is if I have a FQDN with a Port Number already determined, 
will it go through the Procedure of NAPTR/SRV/A query (or) simply do a A query 
(or) Is this left to the client to apply the Logic?

The client must supply the logic. DNS is conceptually a simple database service 
- ask a question, get an answer. The logic of using NAPTR records, SRV records, 
A records,  records, and CNAME records is mostly handled by the client. 
(CNAME and DNAME records are the primary exception, triggering extra processing 
on the recursive name server.)

Chris
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Re: FW: SRV Request to DNS

[Matus UHLAR - fantomas]

On 06.10.15 09:21, Harshith Mulky wrote:

Let us say we are having a FQDN and we need to Resolve it. It goes through
the procedure of determining the IP and Port using NAPTR/SRV/A query
mechanisms


no, the ordinary resolution does NOT use NAPTR and SRV records, only A
and/or  records.


The question I have is if I have a FQDN with a Port Number already
determined, will it go through the Procedure of NAPTR/SRV/A query (or)
simply do a A query (or) Is this left to the client to apply the Logic?


DNS does NOT care about port numbers. 
Some upper-level protocols do, but they must take care themselves.


please provide more detailesd question, or search archives if it hasn't been
answered already.

--
Matus UHLAR - fantomas, uh...@fantomas.sk ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
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in first quarter of year 1901
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FW: SRV Request to DNS

[Harshith Mulky]

Hi all,

I had a query

Let us say we are having a FQDN and we need to Resolve it. It goes through the 
procedure of determining the IP and Port using NAPTR/SRV/A query mechanisms

The question I have is if I have a FQDN with a Port Number already determined, 
will it go through the Procedure of NAPTR/SRV/A query (or) simply do a A query 
(or) Is this left to the client to apply the Logic?

Thanks

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Re: SRV Request to DNS

[Ray Bellis]

On 29/09/2015 07:37, Harshith Mulky wrote:
> Hi all,
> 
> I had a query
> 
> Let us say we are having a FQDN and we need to Resolve it. It goes
> through the procedure of determining the IP and Port using NAPTR/SRV/A
> query mechanisms
> 
> The question I have is if I have a FQDN with a Port Number already
> determined, will it go through the Procedure of NAPTR/SRV/A query (or)
> simply do a A query (or) Is this left to the client to apply the Logic?

NAPTR / SRV are most commonly used when all you have is a "domain name"
and you need to determine the hostname and port associated with a
particular service at that domain (e.g. a SIP server)

I would therefore expect that given a specific hostname and port that
those would be used directly, rather than using NAPTR / SRV.

Ray


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SRV Request to DNS

[Harshith Mulky]

Hi all,

I had a query

Let us say we are having a FQDN and we need to Resolve it. It goes through the 
procedure of determining the IP and Port using NAPTR/SRV/A query mechanisms

The question I have is if I have a FQDN with a Port Number already determined, 
will it go through the Procedure of NAPTR/SRV/A query (or) simply do a A query 
(or) Is this left to the client to apply the Logic?

Thanks
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